1. Field of the Invention
The present invention generally relates to image display systems and more particularly, to an image display system for displaying images using a plurality of display apparatuses.
Recently, users of a personal computer often run a plurality of programs such as a word processor or a spread sheet simultaneously or have a plurality of sets of data displayed on the screen. In such a type of usage, the content to be displayed may be so voluminous that the display area of a single display device proves insufficient. For this reason, systems provided with a plurality of display devices are sometimes used.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 62-229325 and Japanese Laid-Open Patent Application No. 62-256125 disclose methods for displaying a cursor in a system provided with a plurality of display device.
FIG. 1 shows a coordinate system used in Japanese Laid-Open Patent Application No. 62-229325. As shown in FIG. 1, in Japanese Laid-Open Patent Application No. 62-229325, the position of the pointer is updated within the same coordinate system shared by a CRT 1 and a CRT 2.
FIG. 2 is a flowchart showing an algorithm of a process according to Japanese Laid-Open Patent Application No. 62-229325.
As shown in FIG. 2, the pointer position is updated in step S202 without making any distinction between the CRT 1 and the CRT 2.
FIG. 3 shows a coordinate system used in Japanese Laid-Open Patent Application No. 62-256125.
As shown in FIG. 3, in Japanese Laid-Open Patent Application No. 62-256125, the position of a mouse cursor is updated within the same coordinate system (referred to as BMM in Japanese Laid-Open Patent Application No. 62-256125) shared by the CRT 1 and the CRT 2.
FIG. 4 is a flowchart showing an algorithm of a process according to Japanese Laid-Open Patent Application No. 62-256125.
As shown in FIG. 4, the cursor coordinate is calculated in step S2 without making any distinction between the CRTs.
The related art disclosed in Japanese Laid-Open Patent Application No. 62-229325 and No. 62-256125 does not assume a case where the number of pixels (pixel count) and a pixel pitch (pixel-to-pixel pitch) differ from one display device (CRT or the like) to another. In other words, the related art does not provide for a process whereby the cursor movement per a mouse input differs from one display device to another in a system where a plurality of display devices characterized by different pixel count and pixel pitch are used. Such an arrangement has a disadvantage in that the cursor cannot be moved smoothly between the plurality of display devices.
One type of problem (first problem) related to movement of the cursor is caused by failure to provide a method for updating a cursor display position for each display device. Another type of problem (second problem) is caused by failure to adapt for a cursor movement between different means of display by updating the cursor depending on the display means and the displayed position.
A description will now be given of these problems, by contrasting the problems with requirements of users operating a pointing device such as a mouse in a system in which a plurality of display devices are used.
The first problems will now be divided into aspects 1(a), 1(b) and 1(c).
The aspect 1(a) of the first problem is caused even when the plurality of display devices have identical characteristics (pixel count, pixel pitch etc.) and concerns a user request that the cursor movement be adapted for the displayed content in respective display devices. The aspects 1(b) and 1(c) concern a user request that the cursor be moved in a regular manner from one display device to another even when the display devices have different characteristics.
A description will now be given of the details of the individual aspects.
According to aspect 1(a), the cursor movement (velocity) cannot be selectively set for individual display devices. In a system using a plurality of display devices, the displayed content may be varied from one display device to another. For example, one display device could be dedicated to display of documents, while another display device could be dedicated to display of diagrams. Finer pointing is required in the display device dedicated to display of diagrams than in the display device dedicated to display of documents. A requirement exists that the mouse cursor be moved slower in the display device dedicated to diagrams than in the display device dedicated to documents in order to enable finer pointing.
However, no technology has been available to vary a relationship between an output signal of a pointing device and a distance between cursor display positions before and after the movement (the number of pixels by which the positions are offset from each other).
According to aspect 1(b), it is impossible to ensure that, given the same physical movement of the mouse, the distance on one display device between cursor display positions before and after the movement is the same as the corresponding distance on another display device. A requirement exists, particularly in those cases where similar tasks are carried out using a plurality of display devices, that the physical distance that the cursor moves on one display device be the same as the corresponding distance on another display device, given the same mouse movement. According to such a requirement, it is desired that the mouse pointer exhibits a 5 cm on-screen movement both in the display device D1 and in the display device D2, when the mouse is moved 15 cm, for example.
FIG. 5 illustrates aspect 1(b) of the related art. Referring to FIG. 5, a display system includes display devices D31 and D32, a computer 21, a keyboard 22 and a mouse 23.
As indicated by the arrows A1 and A2, a given movement of the mouse 23 do not cause the pointer to move the same on-screen distance on the display device D31 and on the display device D32 if the pixel pitches of the display devices D31 and D32 are different.
According to aspect 1(c), it is impossible to match the rate of a cursor movement on one display device with the corresponding rate on another display device. A requirement exists, when a plurality of display devices are used, that the rate of a mouse cursor movement be the same from one display device to another. For example, assuming that the cursor can be moved end to end on a display device D1 when the mouse is moved 15 cm, users may desire that the cursor on another display device D2 be also moved end to end. While aspect 1(b) concerns matching of the distances, aspect 1(c) concerns the rate of the on-screen pointer movement.
An operator using a mouse may often have an image of how far the mouse should be moved in order to move the pointer from one end of the screen to another. Such an operator may find a system difficult to use if the pointer moves end to end on one display device and only moves 1/3 of the width of the screen on another display device, when the mouse is moved 15 cm. Stated otherwise, such a user may want the pointer to move at a regular rate on the screen instead of wanting the pointer to move the same distance on different display devices in response to the same mouse operation.
FIG. 6 illustrates aspect 1(c) of the related art. In FIG. 6, those components that are the same as the corresponding components in FIG. 5 are designated by the same reference numerals and the description thereof is omitted.
Referring to FIG. 6, a display system includes display devices D41 and D42 characterized by different pixel counts. The display device D41 is a 640.times.480 pixel display and the display device D42 is a 1600.times.1200 pixel display.
As indicated by the arrows B1 and B2, the same physical movement of the mouse causes the cursor to move end to end in the display device D41 but causes the cursor to move only a certain distance on the display device D42.
A description will now be given of the second problem.
According to the second problem, the cursor position changes differently depending on its position on the screen. A requirement exists that such a difference be eliminated.
More specifically, users having such a requirement and using two display devices arranged horizontally may want the cursor to change its display position in a regular manner when the cursor moves from the top of screen and when it moves from the bottom thereof.
FIG. 7 illustrates the second problem of the related art. Referring to FIG. 7 those components that are the same as the corresponding components are designated by the same reference numerals and the description is omitted.
As indicated by the broken lines, when the cursor of the mouse 23 is moved from the display device D41 to the display device D42 or vice versa, the cursor changes its position differently depending on the position of the cursor on a source screen. More specifically, movement of the cursor between point a and point A occurs in orientations different from the corresponding orientations of the movement between point d and point D.
The reason for this irregularity is that, according to the display position calculating method of the related art, the mouse cursor is displayed at the same vertical coordinate before and after the movement from one display device to another. Alternatively, a predetermined value is added to the vertical coordinate on the source display device to determine the vertical coordinate on the destination display device. When the distance between the points a and d on the display device D41 differs from the distance between the points A and D on the display device D42, that difference in the distances is reflected by different vertical positions of the cursor on the display devices D41 and D42. When the number of pixels displayed by the display device D41 is different from that of the display device D42, the cursor moving leftward from point E may not be displayed on the display device D41 at all.